1. Field of the Invention
This invention relates to a continuous centrifuge.
The invention also relates to a basket for the centrifuge.
The invention particularly relates, but is not limited to, a continuous centrifuge (and centrifuge basket therefore) for separating sugar crystals from viscous masses such as molasses or massecuites, while being processed in centrifuges in the production of the sugar crystals.
Throughout the specification, the term “centrifuge” shall also include “centrifugal machine” and “fugal”.
2. Prior Art
In recent years, continuous centrifuges have started to replace batch centrifuges. One reason for this is that the power demands for the continuous centrifuges are more evenly distributed than the “peak” power demands of the batch centrifuges. This enables the capital and operating costs for power supply and transmission equipment to be reduced significantly.
The purging of massecuites in centrifuges has two distinctly separate steps. The first step is the initial removal of all excess molasses and “free” surface molasses from the sugar crystals. The second step is the final washing and partial drying of the crystals before discharge of the crystals from the centrifuge basket. These two steps are presently done with centrifugal single section baskets.
Conventional continuous centrifuges have been proposed with two separate centrifuge baskets. The massecuite feed is directed to a first (upper) basket (for the removal of the “green” molasses) and the resultant sugar crystal/molasses mixture is directed (via deflection means) to a second (lower) basket for the washing of the remaining molasses from the sugar crystals.
When separating the sugar crystals from the massecuites, it is a major objective to minimise the damage to the sugar crystals. The damaged or broken crystals are re-mixed with the molasses/water liquor and must be recrystallised, which is inefficient.
The feeding of the massecuites to the first basket; and the transfer to the second basket, with resultant impacts of the sugar crystals with the baskets and deflection means within the centrifuge, increases the likelihood of damage to the sugar crystals.
The likelihood of damage due to the impacts is increased due to the high gravitational forces within the centrifuge, eg., in the order of 300–1000G. Such high forces are required to cause the molasses to pass through the stainless steel screens in the basket(s) and to be expelled via the drainage holes in the basket(s).
The power demands of the known continuous centrifuges are still relatively high as the baskets must be driven at, eg., 700–2000 rpm to generate the high gravitational forces discussed above. The high power demands at high speed are due to the fact that continuous centrifuge power is proportional to (speed)1.8 to 2.0.